Studies of the tryptophan synthase alpha 2 beta 2 complex serve as a model for studies of more complicated multienzyme complexes. Methods have been developed for the resolution of the holo alpha 2 beta 2 complex and for the dissociation and reassociation of the alpha and beta 2 subunits. Factors which influence subunit association and dissociation are being studied using the methods of gel filtration, difference absorbance, circular dichroism measurements, and enzymatic activity measurements. The results show that pyridoxal 5'-phosphate is tightly bound in the holo alpha 2 beta 2 complex and can only be removed after addition of a salt which causes subunit dissociation. The finding that pyridoxal 5'-phosphate derivatives are much more strongly bound to the alpha 2 beta 2 complex than to the beta 2 subunit indicates that strong binding forces, in addition to the Schiff base linkage, exist in the alpha 2 beta 2 complex but not in the beta 2 subunit. The identification of active site residues and subunit interaction site residues is being investigated using chemical modification and a specific affinity label.